Why is there a different formula for average atomic mass than normal? For example why is the formula (mass)(% abundance) + (mass)(% abundance)/100

Question

anonymous · Answer

alright there is a weighted atomic mass, this happens because you might find  a isotope more commonly than another isotope.

anonymous · Answer

So regardless of the type you take the different isotopes and multiply the mass times the abondances add them all together and get the weighted average